This invention relates to cellular telephones that integrate Global Positioning System (GPS) receivers. More particularly, this invention relates to power management in a cellular telephone.
GPS receiver systems are becoming prevalent among consumers as the GPS system cost decreases and technology allows for the miniaturization of these systems. The popularity of these systems is in large part due to their ability to provide highly accurate position information at a very low cost using a hand-held unit that is small enough to fit in a briefcase or a purse. As a result of this popularity, GPS receiver systems are being integrated into other electronic systems, for example, cellular telephone systems. In this manner, the GPS portion of the electronic system is able to simultaneously provide the position of the cellular telephone user to the user and/or a party that is being communicated with using the integrated cellular telephone. This type of system is typically useful to, but not limited to, emergency services personnel that need to quickly identify the location of a caller, such as an enhanced 911 system.
With regard to electronic systems having integrated GPS systems, emphasis has been placed on the handheld cellular telephone systems because of their prevalent use in society. With the cellular telephone, the battery life of the telephone has a significant impact on the acceptance of a particular model of phone by consumers. Therefore, as the integration of a GPS receiver into a cellular telephone device is likely to increase the power consumption of the telephone device, the telephone designer must focus particular effort on decreasing the power requirements of the integrated telephone device so as to increase the operating time of the device and maximize the availability of the device to a user.
One of the main reasons for the acquisition of a cellular telephone is for use in emergency situations encountered by the user. However, when the cellular telephone is allowed to be used until the battery is dead, the cellular telephone becomes unavailable for emergency use. Prior art cellular telephones fail to automatically provide the reservation of enough power in a cellular telephone battery to allow a 911 emergency call to be placed by the user.
One prior art technique used to provide reserve battery power in other types of portable electronic devices, for example, portable personal computers, is to provide a separate battery for reserve use only. The problem with the use of a spare battery is that, while providing enough power to allow the user to perform a save to the memory before a complete power loss, the battery increases the size and weight of the portable computer.
Another prior art power reservation technique used in portable personal computers is to provide a save-to-disk suspend mode that prevents data loss when the batteries run out of power by copying all system data to a disk drive and turning the computer off. However, prior art cellular telephone systems do not provide an equivalent feature. Thus, the prior art integrated cellular telephone lacks the automatic provision of reserve power for use in placing emergency calls with the cellular telephone.
A method and an apparatus for providing reserve power in a cellular telephone are provided. In one embodiment, reserve power is provided in a portable cellular transceiver comprising a Global Positioning System (GPS) receiver by monitoring, continuously or periodically, a power level of a battery of the portable cellular transceiver. A determination is made as to whether the power level of the battery is greater than a predetermined threshold. Based on the available power level, the portable cellular transceiver is automatically placed into at least one low power mode when the power level reaches a corresponding threshold level. The low power mode may be a shut-off mode which selectively powers down circuitry of the portable cellular transceiver. The corresponding threshold level reserves power for an emergency telephone call. Power is provided to the circuitry of the portable cellular transceiver when the available power level is greater than the predetermined threshold. The reserve power provides power for the activation of the portable cellular transceiver, establishment of a call between the portable cellular transceiver and a cellular base station, transfer of GPS satellite acquisition aiding information to the portable cellular transceiver, receipt of GPS signals, and communication of GPS satellite information (e.g. pseudoranges or a position) to the cellular base station, and, optionally, determination of a position of the portable cellular transceiver.
In an embodiment, the emergency telephone call may be an enhanced 911 call. The emergency telephone call may be a single button call, wherein activation of a single button of the portable cellular transceiver causes the selective application of power to GPS receiver circuitry and selective application of power to communication circuitry. The emergency message may comprise voice data, alphanumeric message data, or some combination of voice and alphanumeric message data.
In an embodiment, the portable cellular transceiver comprises a power detection circuit for monitoring a power level of a battery of the portable cellular transceiver. While the monitoring may be continuous, it may be on a regular basis, a scheduled basis, a predetermined basis, or based on the mode of operation (i.e., stand-by mode or during a phone call). Furthermore, the portable cellular transceiver comprises a power control circuit for automatically placing the portable cellular transceiver into at least one shut-off mode when the power level reaches at least one threshold level. Moreover, the portable cellular transceiver comprises a comparator circuit for determining if a power level of the battery is greater than a predetermined threshold, wherein the power control circuit provides power to at least one circuit of the portable cellular transceiver when the power level is greater than a predetermined threshold.
These and other features, aspects, and advantages of the present invention will be apparent from the accompanying drawings. and from the detailed description and appended claims which follow.